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|Older page:||version 11||Last edited on Sunday, January 9, 2005 3:48:33 pm||by SimonVanderVeken||Revert|
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There are a rats-nest of wires coming out of a PSU. There are large and small four-pin connectors intended for drives. These are called [Berg] connectors, and carry +5V, +12V and two ground wires.
PSUs for computers these days are [ATX] which means they have a unique 20 pin motherboard connector. [ATX] PSUs for Pentium 4 and other recent motherboards have two more connectors to provide 12V and ground to the [CPU]. The cool thing about [ATX] is that the power switch is only 12V and is connected to the mainboard, not the [CPU]. Because [ATX] power supplies are always on, they always supplies a low current to the mainboard in ATX, so don't change ram or IO cards or CPUs without unplugging the mains first. This latter is also a disadvantage as the case and system are no longer grounded to earth through your power cord, so you have to be very carefull with statically sensitive equipment (in case of a computer, everything but the physical chassis/case is a good guideline).
Older PSUs are often [AT], in which there are a pair of motherboard connectors, which are almost always labelled P8 and P9. Sometimes a third connector is present for multi-CPU machines. The biggest irritation for [AT] PSUs is that the power switch is a 240V switch, and is wired to the PSU. An advantage of this is if you turn the computer off, it is off. A disadvantage is that changing the PSU can get fiddly near the power switch, and if you have a dodgy switch may cause a bit of a shock.
Note - [Compaq], [Dell], and [Gateway] are renowned for using strange PSU standards. If you need to replace a PSU in one of those brands then check very carefully. The good news is that the stock PSU is very well engineered. In some cases with these types of machines, it may end up that replacing the case and PSU is a cheaper alternative (as in the case of most [Gateway] computers).